1. Field of the Invention
The present invention relates to a flame retardant aromatic polycarbonate resin composition. More specifically, it relates to a resin composition which comprises (i) resin components including an aromatic polycarbonate resin as the main resin component and a small amount of an acrylonitrile-styrene copolymer, (ii) inorganic fillers including mica having a predetermined particle diameter (C-1) and talc and/or wollastonite (C-2), (iii) an organic phosphorus compound as a flame retardant and (iv) a fluorine-containing compound as a anti-dripping agent, provides (a) a molded article having high stiffness, strength and dimensional accuracy, has (b) satisfactory flame retardancy in spite of a relatively small amount of the flame retardant, and (c) rarely wears away a mold though the inorganic fillers are contained. The resin composition of the present invention is suitable for molding parts which need flame retardancy and high dimensional accuracy, such as chassis and frames.
2. Description of Prior Art
High stiffness, strength and dimensional accuracy (low anisotropy) and excellent flame retardancy are required for plastic materials for use in the chassis or frames (may be simply referred to as “optical unit chassis” hereinafter) of apparatuses having an optical unit, such as laser beam printers, copying machines and projectors. A large number of proposals have already been made for the plastic materials for chassis. Low anisotropy is still strongly required for optical unit chassis. The above various apparatuses having an optical unit have been manufactured for a long time and a lot of know-how has already been accumulated. In the field of the apparatuses having an optical unit under the above situation, new models having higher performance have been developed whereas general-purpose models have been improved, placing stress on a reduction in cost. In this case, plastic materials may have problems with cost required for their molds and the service lives of the molds. That is, a material which rarely wears away a mold (to be referred to as “low mold wearability” hereinafter) is sought for.
A large number of resin compositions suitable for use as molded parts such as chassis and frames have been proposed up till now. (i) JP-A 5-287185 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a resin composition prepared by loading an aromatic polycarbonate resin having a specific molecular weight with a large amount of a glass fiber or the like. And, (ii) JP-A 6-207089 discloses a resin composition which comprises an aromatic polycarbonate resin having a specific molecular weight, a fiber having a non-circular section and a lamellar inorganic filler and achieves low warpage. Further, (iii) JP-A 9-12733 discloses an optical write unit fixing chassis formed from a resin composition which comprises an aromatic polycarbonate resin and mica having a specific particle diameter and a specific thickness. The invention disclosed by JP-A 9-12733 has high stiffness, low warpage and torsion based on low anisotropy, and excellent flame retardancy. That is, it has favorable characteristic properties required for optical unit chassis. However, it is hardly said that molded articles which satisfy all the requirements such as high stiffness, high strength, low anisotropy (high dimensional accuracy), flame retardancy and low mold wearability are obtained from the composition of this invention.
JP-A 1-185360 discloses a resin composition which comprises an aromatic polycarbonate, polycaprolactone and carbon fiber and teaches that the composition has reduced mold wearability. However, the invention disclosed by the above publication does not take into full consideration low anisotropy and fails to disclose technical information on how sufficiently high strength is retained after low anisotropy is achieved.
JP-A 8-115589 discloses a CD-ROM part which comprises a polycarbonate resin, flaky inorganic filler and phosphate compound having a specific structure. However, it is hardly said that the publication discloses a resin composition which satisfies all the requirements such as high stiffness, high strength, excellent flame retardancy and low mold wearability.
JP-A 2001-164105 discloses a resin composition which comprises an aromatic polycarbonate resin, flame retardant, inorganic filler which consists of a glass fiber and talc in a specific ratio and polytetrafluoroethylene having fibril forming capability and teaches that the composition has high stiffness, strength and dimensional accuracy and excellent flame retardancy. However, the composition has room for further improvement as a material for use in models with greater importance attached to a cost reduction.